1. Field of the Invention
The present invention relates to an apparatus for trimming the neck of a blow molded plastic container. More specifically, the present invention relates to a post molding apparatus for trimming a plastic ring from the inner diameter of the neck of a blow molded plastic container to provide a clean circular sealing surface for engagement with a sealing cap.
2. Description of the Prior Art
Plastic containers, such as containers filled with milk and other liquids, are typically blow molded. If the container is blow molded with a blow pin, neck finishing is often accomplished using a pull up or ram down shearing tool on the blow pin. However, some containers are blow molded through use of blow needles and these containers require removal of the container from the blow mold for post mold trimming. During post mold trimming, a blow dome attached to the container is first removed through a guillotine or spin trimming operation. With the blow dome removed, small V-grooves in the inner circumference of the sealing flange of the neck can be seen and are an inherent result of the blow molding process. The V-grooves, located 180.degree. apart (where the pinch-off of the mold halves compress the molten parison) create a disruption in the sealing surface of the container and can cause leakage around the cap.
Two type of caps are typically employed to seal such containers and these include a linerless threaded cap and a snap-on cap. With a linerless threaded cap, the cap is threaded onto the external threads of the container neck and an interiorly formed ring on the cap extends inside of the sealing flange of the container. Preferably, the ring contacts the interior edge of the sealing flange forming a seal closing off the bottle. Clearly, the V-grooves mentioned above might compromise the sealing capability of such a cap. The same is true for snap-on caps. These caps also include an interior ring which extends inside of the sealing flange to engage against the interior edge forming a seal that closes off the container.
In order to ensure that the V-grooves do not compromise the sealing capabilities of the container and cap, the inner diameter of the sealing flange is finished in a post molding operation. Removal of the V-grooves can be done by a reaming and/or facing process. During reaming, a reamer extends into the opening and cuts away portions of the neck flange. However, this generates plastic chips which can enter into the container. The chips must then be removed. Otherwise, the product is contaminated.
In view of the drawbacks and limitations of the prior art, it is seen that there exists the need for a simplified trimming apparatus which provides for a clean inner diameter in the sealing flange of a blow molded container.
It is therefore a principle object of the present invention to provide a trimming apparatus which fulfills that need.
Another object of the present invention is to provide an inner diameter neck trimming apparatus which forms a precise, uniform aperture in the sealing flange of the container without creating chips of plastic material which can potentially enter into the bottle.
A further object of this invention is to provide such a mechanism with a compact construction, minimal complexity, low cost, easy servicing requirements and the potential for retrofiltering into existing machinery.